The present invention relates to improvements in oral care compositions, and more particularly relates to two component foaming oral compositions and methods for the use thereof. Foaming tooth whitening compositions and methods are particular examples hereof.
In the state of the art of oral care compositions and the delivery thereof to the site of use in the oral cavity, many means and methods have been utilized and yet numerous issues remain. For an effective ingredient of an oral care composition to have a therapeutic effect, whether for oral cleaning, treatment or tooth whitening, the effective ingredient must reach and be maintained in effective contact with the oral care feature long enough to provide its intended effect. Thus, dispersion and penetration into and between the surfaces of various oral features such as the odd shapes of the nooks and crannies of adjacent teeth is a continual issue. So too then is the dwell or contact time necessary or at least preferred for having the effective ingredient or ingredients of an oral care composition maintained in contact with or otherwise disposed adjacent the surface of the oral feature being cared for. Such issues arise in various oral cleaning, treatment and/or tooth whitening situations.
In tooth cleaning and/or treatment, effective ingredients such as fluoride or an anti-gingival agent, e.g., triclosan, must reach the areas between teeth or between a tooth and gums and/or reach the nooks and crannies on/of teeth to provide their benefits to those oral features.
Similar activities are necessary in tooth whitening as well. In considering tooth whitening generally, it may first be noted that a tooth is comprised of an inner dentin layer and an outer hard enamel layer that is the protective layer of the tooth. The enamel layer of a tooth is naturally an opaque white or slightly off-white color. It is this enamel layer that can become stained or discolored. The enamel layer of a tooth is composed of hydroxyapatite mineral crystals that create a somewhat porous surface. It is believed that this porous nature of the enamel layer is what allows staining agents and discoloring substances to permeate the enamel and discolor the tooth.
Many substances that a person confronts or comes in contact with on a daily basis can “stain” or reduce the “whiteness” of one's teeth. In particular, the foods, tobacco products and fluids such as tea and coffee that one consumes tend to stain one's teeth. These products or substances tend to accumulate on the enamel layer of the tooth and form a pellicle film on the teeth. These staining and discoloring substances can then permeate the enamel layer. This problem occurs gradually over many years, but imparts a noticeable discoloration of the enamel of one's teeth.
There are available to dentists and consumers many different oral compositions for home and professional in-office use which contain 1-45% by weight concentrations of a peroxygen compound such as hydrogen peroxide and when applied on the teeth may effect whitening of stains. These compositions all require different amounts of time to achieve a desired tooth bleaching effect. These times range from 90 to 120 minutes for a dentist applied, light-activated bleaching system to two weeks or more of over night exposure for tray-delivered whitening products. Currently, even the top selling brands of dentist applied, light activated chair-side tooth whitening systems require a minimum of three (3) twenty-minute applications and an overall minimum of ninety (90) minutes or more to complete when all manufacturers' instructions have been followed.
Among the chemical strategies available for removing or destroying tooth stains, the most effective compositions contain an oxidizing agent, usually a peroxygen compound such as hydrogen peroxide, in order to attack the chromogen molecules in such a way as to render them colorless, water-soluble, or both. In one of the most popular approaches to whitening a patient's teeth, a dental professional will construct a custom-made tooth-bleaching tray for the patient from an impression made of the patient's dentition and prescribe the use of an oxidizing gel to be dispensed into the tooth-bleaching tray and worn intermittently over a period of time ranging from about 2 weeks to about 6 months, depending upon the severity of tooth staining. These oxidizing compositions, usually packaged in small plastic syringes, are dispensed directly by the patient, into the custom-made tooth-bleaching tray, held in place in the mouth for contact times of greater than about 60 minutes, and sometimes as long as 8 to 12 hours. The slow rate of bleaching is in large part the consequence of the very nature of formulations that are developed to maintain stability of the oxidizing composition.
Alternatively, there are oxidizing compositions (generally those with relatively high concentrations of oxidizers) which are applied directly to the tooth surface of a patient in a dental office setting under the supervision of a dentist or dental hygienist. Theoretically, such tooth whitening strategies have the advantage of yielding faster results and better overall patient satisfaction.
Oral compositions for whitening teeth have also been available containing peracetic acid dissolved or suspended in a vehicle. The peracetic acid may have been generated within a dentifrice vehicle by combining water, acetylsalicylic acid and a water soluble alkali metal percarbonate.
Formulations for oxygen liberating compositions for the whitening of teeth have also used either anhydrous and/or hydrated pastes or gels. Hydrated examples include an aqueous oral gel composition comprising about 0.5 to about 10% by weight urea peroxide and 0.01 to 2% by weight of a fluoride providing compound, and/or a water containing a hydrogen peroxide-Pluronic thickened oral gel composition.
Other examples include a toothpaste containing a combination of calcium peroxide and sodium perborate oxidizing agents, dicalcium phosphate, calcium carbonate and magnesium carbonate cleaning agents, sorbitol humectant, cornstarch and cellulose gum thickening agents, and an anionic detergent, and/or oral compositions containing peroxyacids and alkyl diperoxy acids having alkylene groups containing 5-11 carbon atoms for removing stains from teeth.
Yet another conventional example includes administering a light-activated gel under the supervision of a dentist using a protocol of a usual three (3) twenty minute applications. Patients frequently become uncomfortable, agitated and/or bored during such a procedure that typically lasts 1.5 to 2 hours when all set-up and precautionary methods have been included. Also, because of the length of exposure to both the gel and the light, teeth and oral tissues can become irritated or experience a transient hypersensitivity reaction. Thus, any improvement that can result in decreased time, increased patient comfort and increase in bleaching efficiency is desirable.
More specific background information on activating bleaching agents with light energy includes the following. Scientists have identified many kinds of UV photoactivators, which are capable of working in nature to reduce the color of chromophoric stains. These include: transition metal complexes, keto acids, riboflavin, pteridines, algal pigments, cyanocobalamine, thiamin, biotin and aromatic ketones. The pathways by which photo beaching can theoretically occur on tooth surfaces are of two types. First, if the absorption spectrum of the colored chromagen overlaps with the spectrum of incoming radiation, the substrate may undergo photoreaction directly—e.g., the notion of fading color with light. Secondly, and likely a more powerful means for effecting color changes, UV energy may be absorbed by photo activators that then react with tooth surface chromagens, resulting in an “indirect” photobleaching.
Indirect photobleaching may be mediated by transient species (free radicals) that are rapidly consumed by subsequent reactions. For these mechanisms, the rate of reaction is determined by the quantity and type of chromagen, activator, free radicals and incoming UV radiation. Surface gradients involving any of these factors will lead to altered rates of photobleaching at the enamel/bleaching agent interface.
In nature, the major photochemical intermediate free radicals include singlet oxygen, 1O2; superoxide O2-, hydroperoxide HO2° and various other peroxy radicals, RO2. These have been described in more than one hundred patents for the purpose of bleaching teeth. Singlet oxygen free radicals (the most common type of free radical liberated from hydrogen peroxide in the presence of light, heat or most activators), 1O2, are formed primarily through energy transfer from the excited triplet states of dioxygen, 3O2 (as seen in the case of hydrogen peroxide), and wavelengths in the UV-A (315-400 nm) and UV-B (280-315 nm) have been shown to be most effective in their formation. Quantum yields (the fraction or percentage of absorbed photons which give rise to products) range from 1 to 3% and generally decrease with increasing wavelength. Because the high concentrations of hydrogen peroxide or similar compounds are present in tooth bleaching preparations, its decay into water and 1O2 is dominated by this pathway when UV light/activator systems are used in professional tooth bleaching formulas.
The exact mechanism of how these singlet oxygen free radicals come to be formed still remains unclear. Some researchers have suggested that 1O2 is formed by direct electron transfer from the excited triplet states to O2. However, reduction of O2 by radicals or radical ions produced by intramolecular electron transfer reactions, H-atom abstractions and/or homolytic bond cleavages, is equally, if not more plausible. However, it is known that transition metal complexes having one-electron reduction potentials falling between the O2/O2- and O2-/H2O2 couples can rapidly catalyze 1O2 free radical formation.
A commercial application has been made of oxidation from the photo-fenton reaction in which reduced metals such as Fe(II) react with H2O2 and UV light to produce a single OH— radical. This may be because hydroxyl moieties may be generated with less UV activation energy reduction in a chromophoric tooth stain in a given period of time or for a given level of UV energy (the high quantum yield for this reaction is 98%).
These extant methods are not quickly nor highly effective and indeed need prolonged periods for any minimum effective bleaching effects. These time-consuming methods thus suggest that any whitening system that can reduce the time factor is desirable.